Vinyl alcohol polymers (hereinafter vinyl alcohol polymer is sometimes abbreviated as PVA) are one of the few water-soluble and crystalline polymers, and have excellent interfacial and strength properties. PVAs have been used for paper processing, for textile processing, and also as emulsion stabilizers. PVAs also hold an important position as PVA films, PVA fibers, and others.
Block copolymers and graft copolymers comprising chemically bonded polymer units each having different properties show various physical characteristics depending on diverse combination of polymer units. In addition to applications for impact resistant resins, polymeric emulsifiers and dispersing agents, the block copolymers and graft copolymers have attracted attention as film materials and medical materials in recent years, leading to varieties of study cases. Block copolymers comprising a PVA as one of the structural units as well as graft copolymers comprising a PVA as a backbone (trunk polymer) have been expected as new materials having new properties while retaining the properties originated from the PVAs.
Hitherto a block copolymer comprising a PVA as a structural unit has been proposed (Patent Document 1).
Further, some graft copolymers comprising PVAs as backbone have also been proposed (Patent Documents 2 and 3). For example, Patent Document 2 discloses a graft polymer comprising a polyvinyl alcohol (PVA) unit as a main chain and a polymer unit of polymerized sulfonic acid group-containing monomers as a graft chain. This document describes that the graft polymer can be obtained by graft polymerization (or graft reaction) in the presence of a catalyst or an initiator.
Patent Document 3 discloses a method of grafting vinyl monomers on a polyvinyl alcohol comprising: allowing hydroxyl groups as side chains of the polyvinyl alcohol to be reacted with a thiol group-containing silane coupling agent to introduce the thiol groups into the polyvinyl alcohol, subsequently allowing the introduced thiol groups to be reacted with persulfate ions to generate radicals on the polyvinyl alcohol, and allowing the radicals as reacting points to be reacted with the vinyl monomers.
Meanwhile, ion exchange membranes have been used in electrodialysis methods or diffusion dialysis methods for a wide variety of applications such as seawater concentration, removal of salts or nitrate nitrogen from underground brine or brackish water for making drinking water, removal of salts in food production, concentration of active ingredients for medical pharmaceutical product, and others As ion-exchange membranes useful for the above applications, an ion exchange membrane is disclosed which comprises a support layer and an ion-exchange layer formed on the support layer, the ion-exchange layer comprising a block copolymer comprising a polyvinyl alcohol unit and an anionic or cationic polymer unit (Patent Document 4).